This invention concerns a centrifugal pump for pumping liquids containing solid bodies, such as rags and other elongated objects.
The centrifugal pump which draws in the liquid at its center and throws it outwardly in the peripheral direction has good abilities when pumping fairly clean liquids. If the liquid contains solid bodies, however, the problem occurs that these may be stuck between the impeller and the surrounding pump housing and cause a stop or at least a decreased pumping ability.
A method to solve these problems is to design the pump so that the impeller rotates beside the liquid flow, a so-called vortex impeller. The stopping problems are mainly solved by this design, but other disadvantages, such as a decreasing efficiency, occur.
Another method to solve the problem is to arrange some sort of a cutting means in front of the impeller which cuts rags and such things so they become possible to pump. An example of such a construction is shown in U.S. Pat. No. 4,108,386.
In this known design the front end of the impeller is provided with two cutting means, which cooperate with the inlet of the pump housing for cutting up the pollutants. This construction, however, does not work satisfactorily due to the fact that the underpressure prevailing in the pump inlet causes an incoming rag to be drawn into the impeller center. Smaller rags may then rotate with the impeller and never make contact with the cutting means. Bigger rags may bring about an increasing rotation opposition which can stop the pump.